Non-contacting residual stress decay detecting using alternating current stress measurement

Recent work conducted at the Non-Destructive Evaluation Centre of University College London on the residual stress decay detection using the new alternating current stress measurement (ACSM) technology is presented. Flat bar mild steel specimens were used in the experimental study. An equal biaxial compressive residual stress field was introduced into the specimen surfaces by shot peening. The specimens were then subjected to a constant-amplitude cyclic load on a fatigue-testing machine. Under this loading situation, hole-drilling tests indicated that only the residual stress component in the cyclic loading direction had significantly relaxed. Test results showed that this relaxation could be detected by using the existing ACSM system. Further theoretical and experimental efforts are needed to make this technology available for a wide range of practical applications.